Bongo Paired Zooplankton Net

General Information

One of the simplest biological samplers, zooplankton nets are made
in a wide variety of styles and sizes. The two nets in the MARMAP
Bongo vertical-haul net system shown here each have a mouth diameter
of about 25 cm.

History

The historic roots of plankton sampling reach back to the early
19th century when Thomson invented a net he used to sample crab
and barnacle larvae. From this simple collecting device has evolved
an astounding array of instrument types and collecting strategies
for sampling in an immense and often hostile environment. The history
of nets and their use in collecting zooplankton from the world's
oceans, continental shelves, coastal embayments, and freshwater
bodies are almost as varied as the subjects zooplankton biologists
have undertaken to study. An account of the tools that have been
employed to collect zooplankton has been recently prepared by Wiebe
and Benfield (2000), and provides a description of standard sampling
methods. Wiebe and Benfield provide a chronological listing of the
instrument systems and categorized systems presented in the text.

When sampling plankton, an investigator is attempting to answer
two questions in a quantitative way:
1) What living plankton organisms does the sea contain at a given
time?
2) How does this material vary from season and from year to year?
In the early history of ocean sampling, an assumption was made that
plankton were evenly distributed in the oceanic waters and because
of this one could take small samples which would be representative
of large oceanic areas (if the volume of water filtered by the net
could be determined exactly and providing some of the organisms
caught by the net would not escape through the net mesh). This premise
was tested in a variety of ways by many investigators, and many
of the sources of error associated with sampling plankton by nets
and with counting methods to analyze the samples were identified.

Ultimately the research community recognized that there were large
scale spatial variations in the concentration of planktonic forms.
This spatial variability led to a reassessment of sampling that
produced the tools we use today.

The Bongo net was invented in the mid-20th century. Today, bongo
nets are available both in opening/closing and non-closing form.
However, the most commonly used net is a non-closing MARMAP Bongo
Net, developed around 1980.

How It Works

A pulley with a 19 mm diameter chain or cable is used to lower the
nets into the water column. A collecting bucket, attached to the
cod-end of the net, is used to contain the zooplankton sample. Finally,
when the net is retrieved from the ocean, the collecting bucket
can then be detached and easily transported to a laboratory.

The Woods Hole Oceanographic Institution is dedicated to advancing knowledge of the ocean and its connection with the Earth system through a sustained commitment to excellence in science, engineering, and education, and to the application of this knowledge to problems facing society. Learn more »